The invention relates to a drive assembly for moving a drive shaft of a vehicle accessory and, more particularly, to a drive assembly having a hub and a belt-driven pulley which are mounted in interference-fitted relation to the drive shaft.
Many vehicle accessories, such as a hydraulic steering pump, water pump, air injection pump and alternator, are operated by a belt-driven pulley which is attached to the drive shaft of the accessory through a joint capable of transferring a required torque and belt tension load.
With reference to FIG. 1, the conventional arrangement comprises a drive assembly 10 including a hub 12 machined of steel and sized to be press-fitted onto the drive shaft 14 of the accessory 16. A web portion of a belt-driven, sheet metal pulley 18 is affixed to the separate hub 12 at joint 20 by welding, brazing or the like.
In these conventional arrangements, the brazed or welded joint 20 between the hub 12 and the pulley 18 is a potential safety hazard. In the event of joint failure, there is immediate disconnection between the drive shaft 14 and the web portion of the pulley 18. This problem is especially hazardous when the accessory 16 is a power steering pump whereby failure to deliver adequate rotation of the hydraulic shaft results in hydraulic pressure loss which may lead to a sudden increase in steering effort, creating a potentially hazardous condition.
U.S. Pat. No. 4,824,423 discloses a pulley-hub assembly, comprised of two non-machined, sheet metal axial parts, which was intended to provide the operational characteristics of the conventional drive assembly 10 of FIG. 1, at a reduced cost. As shown in FIG. 2, the assembly of U.S. Pat. No. 4,824,423 comprises a pulley 40 having a web or circular wall portion 52 and an axially extending cylindrical wall portion 58 formed integrally from sheet metal defining a cylindrical surface 62. A hub 56 includes an axially extending cylindrical wall portion 64 formed of sheet metal and defining a cylindrical surface 68. An annular flange 66 of the hub is welded to a wall portion 52 of the pulley. However, in certain circumstances, the thin, sheet metal cylindrical wall portions 58 and 64 may exhibit inadequate rigidity in use, and, as a result, do not provide adequate retention at the pulley-shaft connection in the event of failure of the pulley-hub connection. Thus, the construction of this conventional pulley-hub assembly does not provide a solution to the above-mentioned problem.
Accordingly, a need exists to improve a two-part drive assembly so as to satisfy all the current requirements with respect to reliability, safety, reduced weight and cost, and improved overall quality in manufacturing.